Now that Mountain Lion's out with a shiny new version of Safari 6, we thought it time to revisit our browser speed tests. As always, we're pitting the four most popular browsers—this time, on a Mac—against one another in a battle of startup speed, tab loading prowess, and lots more.

We've been testing browsers for awhile, and we've refined our method pretty well. It's a good mix of both manually timed user experience measures and hardcore JavaScript and CSS benchmarks, plus some new tests aimed at features like Chrome's prerendering or Firefox's on demand tab loading can really do. All tests this time around take place on a MacBook Air using a built-in SSD (which is why startup times were so quick). Since it's on a completely different machine and we refine our tests a bit each time, don't compare these numbers to our old tests—just look at the results of the tests we ran this week.

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And, as always, remember that speed is not the only thing each browser has to offer. Each browser has a number of unique features and characteristics, all of which you should factor into making your choice of which to use. However, while most features can be listed on their home pages, you can't easily compare their speed just from each browser's changelog, and that's why we've put this together. It's just one more way to compare the browsers as you make your decision. Also remember that everyone's computer and setup is different, and your numbers may differ from ours depending on your resources, the extensions you use, and the sites you visit, but this should give you a good idea of how each browser handles day-to-day use.

Cold Boot-Up Winner: Safari!

Having an SSD in our computer made all of our browsers start up insanely fast, and it's one of the reasons we recommend an SSD as your next upgrade. However, there were still some differences between each program, with Safari inching in at almost a second to start up. Opera was the only other standout, taking above 1.5 seconds on average.

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Tab Loading Winner: Firefox!

Firefox shockingly took the front spot when it came to loading nine tabs at once, taking a mere 7 seconds to finish loading all nine. Chrome was close behind, with Safari taking about 9 seconds and Opera coming in last place with over 10.

URL Loading Winner: Chrome!

Once again, Chrome's prerendering feature shows its genius, opening pages nearly instantaneously when visited from the menu bar—as long as we had visited that page once during that session. Safari was surprisingly close behind, with Firefox in third place, taking a bit under a second. Opera, on the other hand, didn't fare so well, more than doubling the time of the next slowest browser.

Cold Restore Winner: Opera!

This is still our toughest test. It's designed to test Firefox's on-demand tab loading feature, which aims to make the browser usable more quickly when it restores a large session of tabs. As such, we tried to test a cold restore with nine tabs and stopped the timer when the browser finished its initial "work"—that means Firefox and Opera smoked the others, since they only loaded one or two tabs at a time (and then stopped or loaded the others leisurely), while Chrome and Safari tried to load all of their tabs at once, crushing the browser and making it slow down. Despite Firefox's "load one tab only" approach, Opera still does a fantastic job of loading your first tab and being ready to go in just a few seconds flat.

RoboHornet Winner: Safari!

Mozilla's Dromaeo tests have not only become outdated, but we've started having trouble with crashes trying to run them. So, we're using the brand-new RoboHornet benchmark that's been the buzz around town. It's a community-driven benchmark that tests things like scrolling, canvas, DOM, SVG, and JavaScript to try and give a more accurate, well-rounded picture of your browser's speed. It's still in the early stages, and it's facing lots of praise and a fair amount of criticism. However, that's to be expected as a microbenchmark, and while it isn't the most real-world test, we'd be remiss not to include it. Safari and Chrome came out on top, while Firefox and Opera lagged behind a bit in their tests. for more information on RoboHornet's scoring system, check out this page.

Memory Usage (with Nine Tabs Open) Winner: Safari!

Safari absolutely smoked the other browsers in terms of memory usage. It wasn't very consistent—sometimes it would take up only 50MB or so, other times it would jump up to 100MB—but it was still nowhere near the huge levels of memory the other browsers ate up. Firefox and Opera took up around 300MB, while Chrome gorged itself on over 500MB of RAM.

Memory Usage (with Nine Tabs and Five Extensions) Winner: Safari!

Even with five extensions, Safari absolutely pummeled the other browsers in memory usage. Chrome stayed absurdly high, taking up over a gig of RAM, while Opera gobbled up enough memory to push Firefox into a nice spot at second place.

Overall Scores

As always, overall scores are pretty meaningless, but everyone likes to see a winner. So for those of you handing out trophies, the scores are:

Safari: 78%

Firefox: 64%

Chrome: 60%

Opera: 46%

Safari just rules on the Mac, which is no surprise since it's literally built alongside OS X for optimal operation. Firefox fared surprisingly well, with Chrome not too far behind (except in the memory tests) while Opera took a pretty distant last place. As always, you should look at the individual scores above to see which browser is faster in the areas you care about—if you don't like Firefox's new tabs on demand, for example, Chrome may be "faster" for you in the ways that matter.

Our tests aren't the most scientific on the planet, but they do reflect a relatively accurate view of the kind of experience you'd get from each browser, speed-wise. Let us know if your experience differs-or if the speed losses are worth the browser's other features-in the comments.